<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        textarea {
            margin-top:  20px;
        }
    </style>
</head>
<body>
    <input type="text" id = "txt">
    <input type="button" value="评论" id = "btn"><br />
    <div></div>

    <textarea name="message" id="" cols="30" rows="10"></textarea>

    <script>
        var txt = document.querySelector("#txt");
        var btn = document.querySelector("#btn");
        var tarea = document.querySelector("textarea");
        var odiv = document.querySelector("div");
        btn.onclick = function() {
            odiv.innerHTML += tarea.value;
        }

    </script>
</body>
</html>